Electrical impedance tomography (EIT) is a technique that maps (images) the electrical impedance of an object non-invasively. EIT calculates internal impedance (or conductivity) of the object by applying a known electric current through its surface and then measuring the resulting surface potentials. Although numerous surface electrodes (sometimes hundreds) are used during the procedure, EIT suffers from an inherent low spatial resolution due to the ill-posed nature of the problem. Therefore, EIT has not been widely accepted as a clinical imaging tool.
More recently, there have been efforts to combine EIT with magnetic resonance imaging (MRI) to improve the performance. However, these techniques require complete electrical measurement information from all points inside the object in order to calculate the impedance at a given point within the object. Therefore, these global methods fail when there are areas of missing information inside the object (FIG. 1a on right).
U.S. Pat. No. 6,397,095 B1, issued May 28, 2002 discloses a magnetic resonance-electrical impedance tomography (MREIT) technique for determining the local conductivity of an object. This technique combines magnetic resonance current density imaging (MRCDI) with electrical impedance tomography (EIT). MREIT technique includes a step of current density imaging by placing a series of electrodes around the patient or object to be imaged for the application of current, placing the patient or object in a strong magnetic field, and applying an MR imaging sequence which is synchronized with the application of current through the electrodes. The electric potentials of the surface of the object or patient are measured simultaneously with the MR imaging sequence, as in EIT and the MR imaging signal containing information about the current and the measured potential are processed to calculate the internal impedance of the object or patient. Specifically, the measurements of surface potentials and equipotential lines are used to compute the impedance.